The present invention relates to the preparation of photoactive dye containing silicone polymer compositions. In particular, the present invention is directed to a specific dye-silicone polymer composition in which the dye is present in non-diffusible form thereby rendering the dye containing silicon polymers particularly useful for certain biochemical applications.
The development of glass or plastic fibers, a fraction of a millimeter in diameter, for in vivo biomedical measurements, is a relatively new and important endeavor. Fiber-optic sensors can be as small as electrosensors and offer several distinct advantages. They are safe, involving no electrical connection to the body; the optical leads, very small and flexible, can be included in catheters for multiple sensing; and materials suitable for long term body implantation such as plastic, may be used.
The mechanism of fiber-optic sensor operation is relatively simple. Light from a suitable source travels along an optically conducting fiber to a receptor terminal where reflection, scattering or luminescence occurs. The affected light is then returned to a light measurement instrument which interprets the returned signal. The light emanating from the sensing end of the fiber may be reflected by a tiny transducer that varies the reflectance with some parameter of interest, the light may be back scattered by the medium into which the fiber is inserted, or the returned light may be engendered from luminescence of something at the end of the fiber that was energized by the illuminating light. Of these three general types of in-vivo fiber-optic sensing mechanisms, the luminescence technique has been recently developed as a measurement to determine the amounts of physiological gasses in blood.
The presence of unusually high or low oxygen content in blood samples may indicate various abnormalities. Peterson et al in U.S. Pat. No. 4,476,870 developed an optical sensor for measuring physiological oxygen gas, PO.sub.2. The device is based on the quenching of the fluorescence of certain dyes by oxygen gas. Dyes are chosen for visible light excitation and are distributed on an adsorptive support medium for use as the light scattered terminal for the ingress and egress optical fiber waves. Generally, an inorganic absorbant, such as silica gel, is used in the dye support medium. However, it has been found that such adsorbant materials are humidity-sensitive, thereby seriously interfering with fluorescence at high humidity. The PO.sub.2 optical fiber probe is similar to other gas sensors and reproduces the basic concept of utilizing an indicator packing in a gas permeable container at the end of a pair of optical-fibers.
While the PO.sub.2 probes of Peterson are effective the sensor suffers two disadvantages. First the indicator is a two piece structure comprising a microporous gas permeable envelope which houses a porous packing on which an oxygen quenching dye is adsorbed. As developed by Peterson, these dyes are adsorbed on an organic or inorganic medium and encapsulated in a microporus gas permeable polypropylene envelope. The two part indicator system renders manufacturing more difficult and adsorbants must be carefully selected. As indicated above, inorganic silica adsorbants are ineffective because of their humidity sensitivity. It has also been found that organic adsorbants, such as polystyrene, are deficient in that the dyes from the probe leach out into the blood stream, thereby losing their effectiveness as well as their reusability.
Because of the importance of fiber-optic PO.sub.2 sensors, a need exists to develop or find a unitary indicator comprising a solid gas permeable carrier material which can act as a support medium for the fluorescent dye so that leaching of the dye does not occur during use and the sensor can be used and reused effectively and dependably under any environmental conditions. It is well known that silicone polymers are gas permeable materials having been used in artificial lungs. It has now been found that chemically attaching dyes on certain polysiloxane polymers provides an optimum non diffusible dye indicator system for use in fiber-optic sensors.